I got into a discussion at home about where to best store our bicycle helmets. We store our bikes in the garage (a standalone, not attached to our apartment). So, logically and aesthetically my wife wants to store it in the garage.
My argument against this is that our garage does not temperature control and we live in LA. I think that it can get pretty hot in there during certain times of the year and it can also get cold during other times (winter nights can go down to ~40 F (4.5C)).

My question is whether these temperatures will affect the foam in the helmet in any way. I.e. will it degrade it's ability to provide protection.

6 Answers
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The cold won't hurt it -- foam is used to line refrigerators. And certainly if the temp is going "all the way down" to 40F (shudder!) that's not even close to a problem -- around here it isn't even "cold" unless the temp is below zero F. (In general, solid objects are not damaged by cold, though they do often become more brittle while cold and hence more apt to be damaged while in that state.)

High temps could be a problem, but again foam (very similar to the stuff used in helmets) is used to insulate homes, where attic temps may reach 150F or so, and it's used to insulate water heaters that run at 180F. The problem is that extended high temps over, say, 150F, won't degrade the rigid foam itself, but they will degrade the glues and the foam rubber liner.

That's reassuring Daniel. Are the types of foam different between the architectural applications and the safety application?
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milesmeowDec 15 '11 at 1:17

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Closed-cell foam is primarily polystyrene (Styrofoam), polypropylene, polyisocyanurate, and polyurethane, with some polyethylene and a few other polymers also used. Of those, only polystyrene, polypropylene, and polyurethane are rigid enough to be suitable for helmet shells and the like without some sort of external support. Of course, most helmets now are several layers of different plastics and foams, but the Bell site indicates that the main foam layers of their standard helmets are polystyrene. Polystyrene begins to soften at 90C (194F), but should be stable up to near that temperature.
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Daniel R HicksDec 15 '11 at 4:41

(Polystyrene is not typically used in building and appliance applications because it's too flammable, but it is of course used in ice chests.)
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Daniel R HicksDec 15 '11 at 4:43

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(Note that this means that your helmet is probably at more risk thrown on the back shelf of your car than stored in your garage.)
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Daniel R HicksDec 15 '11 at 12:40

Also, I think that UV radiation (sunlight) will degrade your helmet materials. Another reason not to leave your helmet sitting in the car (near a window) for long periods.
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Dana the SaneJan 3 '12 at 19:45

I would be much more concerned about the potential damage from summer heat than cold.The adhesives used will soften in the heat along with the drying of the foam inserts might comprimize the safety of the helmet.Most manufacturers reccomend storing in a cool dry place out of sunlight.They also suggest replacement after three years of use.Most likely due to the degradation of the materials from sunlight exposure.I would store it in the back of the closet when not in use,an alternative might be to keep it in your cooler if that is stored in the garage as it would be protected from sunlight and more temperature stable even when it is empty.

Not entirely convincing evidence, but Giro's website lists helmets under their cold weather riding section. Also, the Bicycle Helmet Safety Institute website (again, I can't vouch for their statements) list some temperature testing standards by country. These temperatures are generally below freezing, but not as cold as it gets in some regions.

I would say that for regular riding in cold weather, a ski or snowboard helmet may be more appropriate. Not the same type of activity, but the speeds and types of impacts that the helmets are designed for seem close enough.

Yes the cold will affect the foam! OK it's a slightly facetious answer but as you say it's a separate garage how secure is it? In the cold weather the local mice / rodents / what have you will love the foam and use it for bedding material. Make sure it is securely stored otherwise it might get shredded. I speak from experience!

You should also be concerned with the actual storage conditions - most helmet manufacturers recommend replacing an undamaged helmet every x years just because the foam degrades (largely due to UV light). If it's going to be hanging on a wall in direct sunlight there's going to be problems with UV light hitting it, and if you put it away in a dark corner of the garage and it's wet (sweat, condensation, etc.) you'll have issues with mold.

If you absolutely, positively have to store it your best bet may be to find a mesh bag (like they use for laundry), store a single helmet in that, and hang the bag up out of direct sunlight.